Fuel injection control system for in-cylinder injection internal

Details Fuel injection control system for in-cylinder injection internal Fuel injection control system for in-cylinder injection internal

1997-05-19

1998-08-18

Dolinar, Andrew M.

Internal-combustion engines

Combustion chamber means having fuel injection only

Having a particular relationship between injection and...

12317917, F02B 302, F02D 4106

Patent

active

057945861

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a fuel injection control system for an in-cylinder injection internal combustion engine, which system has been devised to improve low-temperature starting characteristics of the in-cylinder internal combustion engine.


BACKGROUND ART

As in-cylinder injection internal combustion engine of the type that fuel is injected directly into a cylinder, diesel engines are widely known. In recent years, the in-cylinder injection type is also available in gasoline engines.
To improve engine performance and reduce emission gas by in-cylinder injection internal engines, those constructed to perform a lean burn operation are furnished.
Fuel injection in such an in-cylinder engine is conducted at the timing shown in the diagram of FIG. 11.
Namely, during an ultra-lean operation, high-pressure fuel injection is performed by a high-pressure fuel pump at a predetermined timing in each compression stroke. During an operation other than such an ultra-lean operation, high-pressure fuel injection is performed by the high-pressure fuel pump at a predetermined timing in each intake stroke.
When an engine-driven pump is used as such a high-pressure fuel pump, no sufficient delivery pressure can be obtained at the time of a start-up of an internal combustion engine because the engine speed is low. To inject fuel at the time of a start-up, low-pressure fuel injection is therefore performed based on a delivery pressure from a low-pressure fuel pump.
When it is intended to achieve both high-pressure injection during an ordinary operation and low-pressure injection at the time of a start-up by a common injector as described above, accurate setting of a flow rate of fuel by the control of a valve-opening period of the injector is needed even when fuel is required in a small quantity under high pressure as in the case of an idling period after a shift to an ordinary operation. This requires to set an injection quantity gain (i.e., a degree of restriction) of the injector so that a low flow rate for an idling period or the like can be set in terms of a valve-opening period which is shortest in view of the responsibility of a solenoid of the injector. When an injection quantity gain suited for such a smallest flow rate is set for the injector, the injection quantity per unit time is limited accordingly. As a result, if fuel is injected at a low pressure as in the case of the time of a start-up, the injection quantity which varies corresponding to a pulse width is limited since the injection quantity per unit time is basically small due to the low-pressure injection. This may lead, for example, to the occurrence of a situation such that a desired injection quantity cannot be attained even if injection is performed during the entire period of an intake stroke as shown in FIG. 11.
Described more specifically, assume that the cranking speed is 100 rpm at low temperatures. The period of each intake stroke then becomes 300 ms, although the injection period required for the injection of fuel in a desired quantity is 420 ms or longer. The injection quantity is therefore considered to become insufficient.
This can also be understood from the diagram of FIG. 10.
In this diagram, against engine speeds plotted along the abscissa, feed air/fuel ratios or fuel injection pulse widths Pw(ms) are plotted along the ordinate. A limit of fuel feeding is shown in a lower part, while a required injection period is indicated in an upper part.
According to the diagram, it is understood that at an engine speed of about 250 rpm or lower, the limit of fuel feeding falls short of the required air/fuel ratio and the fuel injection quantity becomes insufficient.
Describing this matter in a more practical sense, the quantity of fuel required for an engine becomes greater as the engine temperature typified by the coolant temperature or the like becomes lower. Further, the higher the engine speed, the shorter the period of each stroke. Accordingly, low-pressure injection at the time of a start-up may cause a situation such that

REFERENCES:
patent: 5127378 (1992-07-01), Ito
patent: 5598817 (1997-02-01), Igarashi et al.

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